Data storage device and servo information writing method

ABSTRACT

Provided is a data storage device in which read and write heads can be desirably located with respect to servo tracks from the viewpoint of linearity of a PES on the premise that a read write offset exists. A read write offset value, which is a deviation amount between write and read heads in a radial direction of a disk-shaped storage medium, is set equivalent to an integer number N of servo tracks.

BACKGROUND OF THE INVENTION

The present invention relates to a data storage device including arecording medium on which servo information for positioning a read/writehead is written, and more specifically to a data storage device havingcharacteristic servo information written thereto.

A hard disk drive has a magnetic head for reading user data stored on amagnetic disk and for writing user data on the magnetic disk. Themagnetic head is attached to a rotary-type actuator mechanism which isswung by a voice coil motor (VCM).

When the magnetic head writes or reads user data, the actuator mechanismis driven, and thus the magnetic head is moved to a predetermined trackand positioned. Movement of the magnetic head to a predeterminedposition is controlled by using servo information stored on the magneticdisk as a clue.

On a magnetic disk contained in a hard disk drive or the like, aplurality of data tracks are concentrically formed and, moreover,identification information and burst patterns are stored along radialdirections of the disk in advance. The identification information andthe burst patterns constitute servo information. The identificationinformation is information indicating track addresses of respective datatracks. Based on the identification information read by a magnetic head,determination can be made as to an approximate position of the magnetichead, that is, as to which data track a position of the magnetic headcorresponds to. The burst patterns are constituted by a plurality ofburst pattern rows in which areas having signals stored therein arearranged along the radial directions of the disk at constant intervalsand of which signal storage areas have mutually different phases. It ispossible to detect a precise position of the magnetic head, that is, adeviation indicating how far the position of the magnetic head deviatesfrom the data track to which the magnetic head corresponds, based on asignal (position error signal: PES) outputted from the magnetic head inaccordance with the burst pattern.

A read or write of user data with respect to the magnetic disk isperformed in a state where the magnetic disk is rotating after thefollowing operations: the magnetic head is moved while an approximateposition of the magnetic disk is being determined based on theidentification information read by the magnetic head, whereby themagnetic head is made to correspond to a specific data track; and thenthe magnetic head is precisely positioned at the specific data trackbased on a signal outputted from the magnetic head in accordance withthe burst patterns. Such a series of operations are referred to as aseek operation. Even in a period when user data is being read orwritten, feedback control is performed so that the magnetic head ispositioned at a fixed position relative to the specific data track basedon the signal outputted from the magnetic head in accordance with theburst patterns. Such an operation is referred to as a track followingoperation.

Servo information is written on a magnetic disk as a recording medium ina manufacturing process before a hard disk drive is shipped as aproduct. It is required that the servo information be written preciselyin order to write or read user data accurately.

In a hard disk drive, as a recording density increases, amagnetoresistance (MR) head or giant magnetoresistance (GMR) head usingthe magnetoresistance effect is used as a reproducing head (read head),and an inductive head is used as a recording head (write head). The twoheads are attached to a same magnetic head slider and constitute ahybrid magnetic head.

As described above, one existing hard disk drive uses a rotary-typeactuator as an actuator for driving a magnetic head. Therefore, when themagnetic head accesses a predetermined position on a magnetic disk, atrajectory of the magnetic head forms a circular arc. Accordingly, overthe range of the most inner track to the most outer track of themagnetic disk, the center line of a magnetic head slider and a tangentline of a data track on the magnetic disk are not parallel but intersectwith a different angle depending on each data track. The intersectingangle is referred to as a skew angle.

The existence of the skew angle inevitably generates a read write offsetdescribed later. Specifically, when a read head is positioned at aproper position on a servo track of the magnetic disk (such a state isreferred to as “on track”), a write head cannot be positioned at aproper position on the servo track (such a state is referred to as “offtrack”). The position difference between the centers of the read andwrite heads is a read write offset.

In a hard disk drive, when user data is written on a magnetic disk(recording), a magnetic head slider is moved to a target position byreading servo information recorded on a servo track by use of a readhead, the read head is made to be “on track” on a servo track, and thenthe user data is written on a data track of the magnetic disk by a writehead. On the other hand, when the user data written on the data track isreproduced, even if the read head is made to be “on track” on the servotrack, the read head cannot be “on track” on the data track to which thewrite head has written the user data, due to a read write offset.Accordingly, the user data may not be accurately reproduced sometimes.

Various proposals have been made for solving the above-described problembased on a read write offset. Japanese Unexamined Patent Publication No.2000-322848, for example, discloses a method in which a measured readwrite offset value is stored, and an access position is corrected basedon the stored read write offset value when user data is reproduced, thusperforming positioning control of a magnetic head slider.

The above-described proposal is an effective method for a read writeoffset but has the following problems.

FIG. 13 is a view showing a relationship between burst patterns BP and aPES. Ideally, it is preferred that the PES is shown by continuous linearlines. However, in reality, the linearity is lost in regions indicatedby circles and surrounding regions thereof. Therefore, an error appearsin a physical position obtained by conversion based on the PES.Moreover, the loss of the linearity adversely influences a servo controlsystem. In a hard disk drive used heretofore, servo tracks are recordedat a constant track pitch on a magnetic disk. Accordingly, any one ofread and write heads is located at a position where linearity of a PESis lost.

SUMMARY OF THE INVENTION

The present invention has an object to provide a data storage device inwhich read and write heads can be located at a desired position of servotracks from the viewpoint of linearity of a PES with the assumption thata read write offset exists. Another object of the present invention isto provide a servo information writing method for obtaining such a datastorage device.

The present invention proposes a method in which a pitch of servo tracksis not set constant as heretofore, but in which the servo tracks aredivided into zones and the pitch of the servo tracks is varied withineach zone, thereby setting a read write offset value to a valueequivalent to an integer number N of the servo tracks. Thus, both writeand read heads can be positioned at positions where linearity of a PESis maintained.

The present invention is based on the above-described knowledge and is adata storage device including: a disk-shaped storage medium which has adata storage area and a servo area; a hybrid head slider which supportswrite and read heads; and a rotary-type actuator which swings the hybridhead slider to position any one of the write and read heads at a targettrack of the disk-shaped storage medium. The data storage area containsa plurality of data tracks which store user information, and the servoarea contains a plurality of servo tracks which store servo informationfor identifying positions of the plurality of data tracks. The writehead writes user data on the data tracks of the disk-shaped storagemedium, and the read head reads the user data written on the datatracks. In the data storage device, a read write offset value is setequivalent to an integer number N of the servo tracks. Here, the readwrite offset value is a deviation amount between the write and readheads in a radial direction of the disk-shaped storage medium, and thedeviation amount is caused by swinging of the hybrid head slider by therotary-type actuator.

In the data storage device of the present invention, the read writeoffset value can be set equivalent to an integer number N of the servotracks by varying a pitch of the plurality of servo tracks in the radialdirection of the disk-shaped storage medium. In this case, apredetermined number of the servo tracks are regarded as a zone, and theinteger number N can be varied within each zone. Moreover, the integernumber N can be increased stepwise from an inner diameter toward anouter diameter of the disk-shaped storage medium.

According to the data storage device of the present inventionconstituted as described above, the write and read heads can bepositioned within a region where an error signal obtained from the servoinformation is linear, which is preferable for servo control.

Note that the present invention is effective when it is applied to adata storage device in which write and read heads are supported by ahybrid head slider at a predetermined center distance from each other ina radial direction of a disk-shaped storage medium.

In the hard disk drive used heretofore, a pitch of servo tracks isconstant, whereas, in the data storage device of the present invention,the pitch of the servo tracks is deliberately made nonconstant, therebymaking it possible to set the read write offset value to a valueequivalent to an integer number N of the servo tracks. Therefore, thepresent invention provides a data storage device including: adisk-shaped storage medium which has a data storage area and a servoarea, the data storage area containing a plurality of data tracks whichstore user information, the servo area containing a plurality of servotracks which store servo information for identifying positions of theplurality of data tracks; a hybrid head slider which supports write andread heads, the write head writing user data on the data tracks of thedisk-shaped storage medium, the read head reading the user data writtenon the data tracks; and a rotary-type actuator which swings the hybridhead slider to position any one of the write and read heads at a targettrack of the disk-shaped storage medium, and wherein a pitch of theservo tracks varies within a predetermined region in a radial directionof the disk-shaped storage medium.

In the data storage device of the present invention, the pitch of theservo tracks is preferably varied with a standard pitch centered withinthe predetermined region in the radial direction of the disk-shapedstorage medium. In this case, a variation ratio of the pitch of theservo tracks is preferably inverted from plus to minus at a positionwhich has the standard pitch and which is measured along the radialdirection of the disk-shaped storage medium as a boundary.

The present invention also provide a servo information writing methodfor writing a burst pattern as servo information on a disk-shapedstorage medium of a data storage device which has a hybrid headincluding write and read heads. In the writing method, first, a readwrite offset value is measured within a predetermined range on thedisk-shaped storage medium, where the read write offset value is adeviation amount between the write and read heads in a radial directionof the disk-shaped storage medium. Next, the burst pattern is written sothat the measured read write offset value is equivalent to an integernumber N of servo tracks formed by the burst pattern.

In the servo information writing method of the present invention, theburst pattern is preferably written so that a pitch of the servo tracksvaries at a predetermined variation ratio in the radial direction of thedisk-shaped storage medium. Moreover, the pitch of the servo tracks ispreferably varied in relation to a predetermined pitch set as astandard.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a servo trackwriter according to an embodiment.

FIG. 2 is a view schematically showing stored contents of a magneticdisk according to the embodiment.

FIG. 3 is another view schematically showing the stored contents of themagnetic disk according to the embodiment.

FIG. 4 is a view showing a state of a magnetic head slider swinging overthe magnetic disk.

FIGS. 5A to 5C are views showing arrangements of write and read heads Wand R in the magnetic head slider.

FIG. 6 is a view schematically showing a state of the magnetic headslider positioned at the most inner track (ID) of the magnetic disk.

FIG. 7 is a view schematically showing a state of the magnetic headslider positioned at the most outer track (OD) of the magnetic disk.

FIG. 8 is a view schematically showing a positional relationship among aposition of the write head, a rotation center (SP) of the magnetic disk,and a pivot center (PV).

FIG. 9 is a graph showing a relationship between a position in a radialdirection of the magnetic disk and a value obtained by dividing a readwrite offset value by a standard servo track pitch Pn in a hard diskdrive according to the embodiment.

FIG. 10 is a graph showing a relationship between variation of a servotrack pitch and the position in the radial direction of the magneticdisk in the hard disk drive according to the embodiment.

FIG. 11 is a graph showing a relationship between the position in theradial direction of the magnetic disk and the read write offset value inthe hard disk drive according to the embodiment.

FIG. 12 is a view for explaining an advantage inherent in the hard diskdrive according to the embodiment.

FIG. 13 is a view showing a relationship between burst patterns and aPES.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the present invention will be described based on anembodiment.

FIG. 1 is a view schematically showing a hard disk drive 2 according tothe embodiment and a servo track writer 1 for performing a write ofservo information to the hard disk drive 2.

The servo track writer 1 is a device which has a recording controller 8,a head positioner 9, and a positioner controller 10, and which writesservo information on a magnetic disk 3 constituting the hard disk drive2.

The hard disk drive 2 has a magnetic disk 3 on which user data is to bewritten, a spindle motor 4 for driving rotation of the magnetic disk 3,a magnetic head slider 5 which supports a write head for writing userdata on the magnetic disk 3 and a read head for reading user datawritten on the magnetic disk 3, an arm 6 for supporting the magnetichead slider 5, and a voice coil motor 7 for swinging the arm 6. Whenuser data is written to or read from the magnetic disk 3 in the harddisk drive 2, the magnetic head slider 5 is swung over the magnetic disk3 by the voice coil motor 7. Note that the hard disk drive 2 may have aplurality of magnetic disks 3 but only one magnetic disk 3 is shown inFIG. 1. The servo track writer 1 writes servo information on themagnetic disk 3 by using the magnetic head slider 5 of the hard diskdrive 2.

A plurality of tracks are concentrically formed on the magnetic disk 3.The tracks are each divided into a plurality of sectors in which servosectors and data sectors are paired. A servo sector is an area on whichservo information for identifying a position on the tracks is stored.The servo information is written by the write head supported by themagnetic head slider 5. A write of servo information will be describedlater.

When the hard disk drive 2 is operating, the rotation of the magneticdisk 3 is driven around a spindle shaft of the spindle motor 4. On theother hand, when the hard disk drive 2 is not operating, the rotation ofthe magnetic disk 3 is stopped (stationary). On each recording surfaceof the magnetic disk 3, a plurality of servo track areas 30 are radiallyformed along radial directions (directions of Arrows B in FIG. 2) of themagnetic disk 3 as shown in FIG. 2, and other areas are set to be datatrack areas 32. Part of the servo track areas 30 and the data trackareas 32 are shown in FIG. 3. In the data track areas 32, a plurality ofdata tracks are concentrically formed at a predetermined pitch. Datatracks 34A, 34B, 34C, and 34D, which are part of the plurality of datatracks, are shown in FIG. 3. Read and write of user data are performedwith respect to the data tracks 34 along a circumferential direction(direction of Arrow A in FIGS. 2 and 3) of the magnetic disk 3 by themagnetic head slider 5 described later.

On the other hand, in the servo track areas 30, track identificationinformation storage areas 30A and burst pattern storage areas 30B areprovided. In the track identification information storage areas 30A,track identification information in which a track address of each datatrack 34 is represented by a gray code (cyclic binary code) is storedcorresponding to each data track 34. In the burst pattern storage areas30B, burst patterns are formed. As shown in FIG. 3, the burst patternsare constituted by four burst pattern rows (burst pattern rows A to D).In each burst pattern row, areas each having a signal stored therein(portions indicated by hatching in FIG. 3) are arranged along anarranging direction of the data tracks 34, that is, the radial direction(direction of Arrow B in FIG. 3) of the magnetic disk 3. Each signalstorage area constituting each burst pattern row has a length along theradial direction of the magnetic disk 3 and a distance from the signalstorage area adjacent thereto which are each equal to a pitch DP of thedata tracks 34 in length. Moreover, as shown in FIG. 3, a width of asingle burst pattern constitutes a pitch SP of a single servo track.

When the magnetic head slider 5 is used as part of the hard disk drive 2as described above, it performs a write or read of user data withrespect to the magnetic disk 3. Meanwhile, when the magnetic head slider5 functions as part of the servo track writer 1, it writes servoinformation on a servo track.

When servo information is written on a predetermined servo track, thehead positioner 9 guides the magnetic head slider 5. Moreover, the headpositioner 9 also has a positioning function for stopping the magnetichead slider 5 at a predetermined position after guiding the magnetichead slider 5 to the relevant position. The head positioner 9 drives themagnetic head slider 5 based on instructions from the positionercontroller 10.

The recording controller 8 controls a write of servo informationperformed by the magnetic head slider 5. Moreover, the recordingcontroller 8 instructs the positioner controller 10 to drive the headpositioner 9. The positioner controller 10 controls operations of thehead positioner 9 based on the instructions.

Next, a write of servo information to the magnetic disk 3 will bedescribed. Note that the write processing of servo information isperformed by the recording controller 8, the head positioner 9, thepositioner controller 10, and the write head, which is supported by themagnetic head slider 5.

As shown in FIG. 4, the arm 6 holding the magnetic head slider 5 movescircularly about a pivot center PV by the voice coil motor 7. Apositional relationship among the magnetic disk 3, the arm 6, and thevoice coil motor 7 is fixed so that a skew angle becomes zero when themagnetic head slider 5 is at the center in the radial direction of themagnetic disk 3, for example.

FIGS. 5A to 5C show arrangements of the write and read heads W and R inthe magnetic head slider 5. Note that FIGS. 5A to 5C are plan views inwhich the magnetic head slider 5 is viewed from the top surface thereof.In the magnetic head slider 5 in FIG. 5A, the write and read heads W andR are located at a predetermined center distance from each other in theradial direction of the magnetic disk 3. In addition, the write and readheads W and R are arranged so as to be away from each other by adistance T in the longitudinal direction of the arm 6 and a distance Iin the transverse direction of the arm 6. Hereinafter, description willproceed using the magnetic head slider 5 shown in FIG. 5A as an example.

FIG. 6 schematically shows the state where the magnetic head slider 5 ispositioned at the most inner track (ID) of the magnetic disk 3, and FIG.7 schematically shows the state where the magnetic head slider 5 ispositioned at the most outer track (OD) of the magnetic disk 3. In FIG.6, [alpha]1 denotes the angle between the segment L1 which connects thecenter of the write head W in the width direction thereof and the pivotcenter PV and the tangent line L2 which touches the track located on IDat the center of the write head W. Moreover, in FIG. 6, [beta]1 denotesthe angle between the segment L1 connecting the center of the write headW in the width direction thereof and the pivot center PV and the segmentL3 connecting the center of the write head W and the rotation center ofthe magnetic disk 3. On the other hand, in FIG. 7, [alpha]2 denotes theangle between the segment L1 which connects the center of the write headW in the width direction thereof and the pivot center PV and the tangentline L2 which touches the track located on OD at the center of the writehead W. Furthermore, in FIG. 7, [beta]2 denotes the angle between thesegment L1 connecting the center of the write head W in the widthdirection thereof and the pivot center PV and the segment L3 connectingthe center of the write head W and the rotation center of the magneticdisk 3.

FIG. 8 is a view schematically showing an arrangement relationship amongthe position WHP of the write head W, the rotation center SP of themagnetic disk 3, and the pivot center PV. Note that, as shown in FIG. 8,A denotes the segment connecting the pivot center PV and the rotationcenter SP of the magnetic disk 3, B denotes the segment connecting thepivot center (PV) and the position (WHP) of the write head W, and Cdenotes the segment connecting the rotation center (SP) and the position(WHP) of the write head W. The segment C identifies the distance fromthe center of the magnetic disk 3 to the write head W in the radialdirection of the magnetic disk 3 (hereinafter, such a distance isreferred to as a position in the radial direction).

Based on FIGS. 6 and 7, a read write offset value when the magnetic headslider 5 is positioned at ID (hereinafter, such a read write offsetvalue is sometimes abbreviated to OFSID) and a read write offset valuewhen the magnetic head slider 5 is positioned at OD (hereinafter, such aread write offset value is sometimes abbreviated to OFSOD) can berespectively found from Equations 1 and 2 shown below.OFSID=T sin(α1)+I cos(α1)  Equation 1OFSOD=T sin(−α2)+I cos(−α2)  Equation 2

Moreover, in FIG. 8, the angle [beta] can be found from Equation 3 shownbelow by using the cosine theorem. Furthermore, based on FIGS. 6 and 7,the relationship between [alpha] and [beta] can be expressed by Equation4 shown below. Therefore, the angle [alpha] for a position in the radialdirection of the magnetic disk 3 can be found.β=arc cos{(B ² +C ² −A ²)/2BC}  Equation 3β−π/2=α  Equation 4

Here, when the number of the magnetic head sliders 5 is more than one, Tand I in FIG. 5A are variables which vary depending on the respectivemagnetic head sliders 5. Accordingly, if the read write offset value ismeasured at ID and OD, then simultaneous equations including Equations 1and 2 are solved to obtain T and I specific to each magnetic head slider5.

Moreover, based on Equations 3 and 4, C can be found from Equation 5below. Furthermore, based on Equation 1, [alpha] can be found fromEquation 6 below.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack & \; \\{C = {\frac{1}{2}\left( {{2\; B\;{\cos\left\lbrack {a + \frac{\pi}{2}} \right\rbrack}} + \sqrt{\left( {2B\;{\cos\left\lbrack {a + \frac{\pi}{2}} \right\rbrack}} \right)^{2} - {4\left( {B^{2} - A^{2}} \right)}}} \right)}} & {{Equation}\mspace{14mu} 5} \\\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack & \; \\{a = {\arcsin\left\lbrack {\frac{1}{T^{2} + I^{2}}\left( {{{RWOFS} \times T} - {I\sqrt{T^{2} - I^{2} - {RWOFS}^{2}}}} \right)} \right\rbrack}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

The position C can be found from Equations 5 and 6 by using T and Iobtained above and applying the read write offset value (hereinafter,sometimes abbreviated to RWOFS) to Equations 5 and 6. Note thatC=f(RWOFS) is described as C(RWOFS).

A standard servo track pitch is now denoted by Pn. All the positions Cwere obtained when RWOFS is N times Pn (N is an integer number) and Ntimes Pn+/−0.5. The result is shown in FIG. 9. FIG. 9 is a graph withthe position C (Radius: mm) in the radial direction of the magnetic disk3 on the horizontal axis, and with the value obtained by dividing RWOFSby the standard servo track pitch Pn on the vertical axis. Note that, inFIG. 9, the positions C when RWOFS is N times the standard servo trackpitch Pn are represented by white circles, and the positions C whenRWOFS is N times the standard servo track pitch Pn+/−0.5 are representedby black circles. Incidentally, the reason for adding the sign −(minus)to the vertical axis in FIG. 9 is because the write head W is used as astandard and the directions of OD and ID are respectively designated asplus and minus.

For the position C(Pn×n1) when N=n1, that is, when RWOFS=Pn×n1, thestandard servo track pitch Pn is varied within the range of C(Pn×n1−0.5)to C(Pn×n1+0.5) in accordance with Equation 7 below.Pnew=Pn×(Pn×n1/(Pn×n1+a))  Equation 7Here, a is +/−0.5.

From Equation 7, the servo track pitch Pnew becomes maximum atC(Pn×n1−0.5) and becomes minimum at C(Pn×n1+0.5). Similarly, for all thenumbers N, the variation ratio (Track Pitch variation ratio) when thestandard servo track pitch Pn is varied is obtained. The relationshipbetween the variation ratio and the position in the radial direction ofthe magnetic disk 3 is shown as FIG. 10. As shown in FIG. 10, the servotrack pitch Pnew varies over the range of ID to OD of the magnetic disk3 and is nonconstant. Moreover, FIG. 10 shows that the servo track pitchPnew is the standard servo track pitch at the positions where thevariation ratio is zero, and that the servo track pitch Pnew varies withthe standard servo track pitch as a center. In addition, it can be seenthat the variation ratio is inverted from plus to minus (or from minusto plus) at the boundary positions in the radial direction where thevariation ratio is zero.

FIG. 11 shows the relationship between the position in the radialdirection of the magnetic disk 3 and the read write offset value whenthe servo track pitch is varied as shown in FIG. 10. Note that the readwrite offset value is shown as the number of servo tracks (Offset inservo track). As shown in FIG. 11, if the servo track pitch is varied asshown in FIG. 10, then the read write offset value for each position inthe radial direction of the magnetic disk 3 becomes a value equivalentto N servo tracks which are each varied, where N is an integer number.Note that, as shown in FIG. 11, the read write offset value representedas a value equivalent to N servo tracks is constant within apredetermined range in the radial direction. That is, the servo tracksare divided into zones, and the servo track pitch is set so that theread write offset value becomes a value equivalent to N servo trackswhich exist in each zone. The integer number N varies depending on thezones and, in particular, increases from ID toward OD stepwise.

According to the hard disk drive 2 having the read write offset value asshown in FIG. 11, both the write and read heads W and R are positionedat positions where linearity of a PES is maintained. Such positions arepreferable for position control by a servo as described above. Theabove-described advantage according to the embodiment will be describedbelow based on FIG. 12.

FIG. 12 is a view in which the read write offset values and the servotracks are shown while being compared to each other. In FIG. 12, threecases where the read write offset values differ from each other aredrawn. Note that the read head R is common to the three cases. Burstpatterns such as A, B, and the like drawn in FIG. 12 are drawn assumingthat the servo track pitch is constant for convenience.

In FIG. 12, the cases I and II show the cases where the read writeoffset values are equivalent to N servo tracks. The case I shows thecase of seven servo tracks and the case II shows the case of eight servotracks. In the case I, the read head R is positioned on the boundarybetween the servo tracks C3 and D3, and the write head W is positionedon the boundary between the servo tracks B1 and A2. In the case II, theread head R is positioned on the boundary between the servo tracks C3and D3, and the write head W is positioned on the boundary between theservo tracks C1 and D1. As can be seen from the foregoing descriptionbased on FIG. 13, in the cases I and II, both the read and write heads Rand W are positioned at positions desirable for positioning control.

In contrast with the cases I and II described above, in the case IIIwhere the read write offset value is not equivalent to N servo tracks,the write head W is positioned within the servo track constituted by theservo patterns B1 and C1. Therefore, as can be seen from the descriptionbased on FIG. 13, the write head W is positioned at a positionundesirable for positioning control.

As described above, in the hard disk drive 2 according to theembodiment, the read write offset value can be set to a value equivalentto N servo tracks by adjusting the servo track pitch. Accordingly, theread and write heads R and W can be positioned at positions desirablefor servo control.

In the embodiment described above, the arrangement of the read and writeheads R and W was described using the example of FIG. 5A, but theapplication of the present invention is not limited to this aspect. Itis needless to say that the present invention can be applied to either amagnetic head slider 5 in which the centers of read and write heads Rand W are aligned like FIG. 5B or a magnetic head slider 5 in which readand write heads R and W are parallelly located at a predetermined centerdistance from each other in the radial direction of the magnetic disk 3as shown in FIG. 5C, for example. In the magnetic head slider 5 as shownin FIG. 5C, in which the read and write heads R and W are locatedparallelly, the read write offset value is larger, thus making theapplication of the present invention more effective.

When a write or read of user data is performed in the hard disk drive 2according to the embodiment, operations of the magnetic head slider 5can be controlled in a similar manner to that described in thebackground art. A table having read write offset values corresponding torelevant positions of a data track on the magnetic disk 3 prepared inadvance, for example. When user data is written on the relevant datatrack and then read, the read head R is moved by an amount of the readwrite offset value obtained by referring to the table, thus making itpossible to appropriately read the user data.

As described above, the present invention provides a data storage devicein which read and write heads can be desirably located with respect toservo tracks from the viewpoint of linearity of a PES by setting a readwrite offset value to a value equivalent to N servo tracks.

Although the preferred embodiment of the present invention has beendescribed in detail, it should be understood that various changes,substitutions and alternations can be made therein without departingfrom spirit and scope of the inventions as defined by the appendedclaims.

1. A data storage device comprising: a disk-shaped storage medium whichhas a data storage area and a servo area, the data storage areacontaining a plurality of data tracks which store user information, theservo area containing a plurality of servo tracks which store servoinformation for identifying positions of the plurality of data tracks; ahead slider which supports write and read heads, the write head writinguser data on the data tracks of the disk-shaped storage medium, the readhead reading the user data written on the data tracks; and a rotary-typeactuator which swings the head slider to position any one of the writeand read heads at a target track of the disk-shaped storage medium,wherein a pitch of the plurality of servo tracks is varied in the radialdirection of the disk-shaped storage medium, and a read write offsetvalue is thereby set equivalent to an integer number N of the servotracks, the read write offset value is set equivalent to an integernumber N of the servo tracks, the read write offset value being adeviation amount between the write and read heads in a radial directionof the disk-shaped storage medium, the deviation amount being caused byswinging of the head slider by the rotary-type actuator.
 2. The datastorage device according to claim 1, wherein the plurality of servotracks are divided into zones, and the read write offset value isequivalent to a constant number of servo tracks that exist in each zone.3. The data storage device according to claim 1, wherein the integernumber N varies with each predetermined number of the servo tracks.
 4. Adata storage device comprising: a disk-shaped storage medium that has adata storage area and a servo area, the data storage area containing aplurality of data tracks that store user information, the servo areacontaining a plurality of servo tracks that store servo information foridentifying positions of the plurality of data tracks; a head sliderthat supports write and read heads, the write head writing user data onthe data tracks of the disk-shaped storage medium, the read head readingthe user data written on the data tracks; and a rotary-type actuatorthat swings the head slider to position any one of the write and readheads at a target track of the disk-shapes storage medium, wherein aread write offset value is set equivalent to an integer number N of theservo tracks, the read write offset value being a deviation amountbetween the write and read heads in a radial direction of thedisk-shaped storage medium, the deviation amount being caused byswinging of the head slider by the rotary-type actuator, wherein theinteger number N increases stepwise from an inner diameter toward anouter diameter of the disk-shaped storage medium.
 5. A data storagedevice comprising: a disk-shaped storage medium that has a data storagearea and a servo area, the data storage area containing a plurality ofdata tracks that store user information, the servo area containing aplurality of servo tracks that store servo information for identifyingpositions of the plurality of data tracks; a head slider that supportswrite and read heads, the write head writing user data on the datatracks of the disk-shaped storage medium, the read head reading the userdata written on the data tracks; and a rotary-type actuator that swingsthe head slider to position any one of the write and read heads at atarget track of the disk-shaped storage medium, wherein a read writeoffset value is set equivalent to an integer number N of the servotracks, the read write offset value being a deviation amount between thewrite and read heads in a radial direction of the disk-shaped storagemedium, the deviation amount being caused by swinging of the head sliderby the rotary-type actuator, wherein the write and read heads arepositioned within a region where an error signal obtained from the servoinformation is linear.
 6. The data storage device according to claim 5,wherein the write and read heads are supported by the head slider whilebeing located at a predetermined center distance from each other in theradial direction of the disk-shaped storage medium.
 7. A servoinformation writing method for writing a burst pattern as servoinformation on a disk-shaped storage medium of a data storage devicewhich has write and read heads, comprising the steps of: calculating aread write offset value within a predetermined range on the disk-shapedstorage medium, the read write offset value being a deviation amountbetween the write and read heads in a radial direction of thedisk-shaped storage medium; and writing the burst pattern so that themeasured read write offset value is equivalent to an integer number N ofservo tracks formed by the burst pattern, wherein the burst pattern iswritten so that a pitch of the servo tracks varies at a predeterminedvariation ratio in the radial direction of the disk-shaped storagemedium.
 8. The servo information writing method according to claim 7,wherein writing the burst pattern so that the measured read write offsetvalue is equivalent to the integer number N of servo tracks formed bythe burst pattern further comprises dividing the servo tracks into zonesso that the read write offset value is equivalent to a constant numberof servo tracks that exist in each of the zones.
 9. The servoinformation writing method defined in claim 7 wherein the integer numberN increases stepwise for an inner diameter toward an outer diameter ofthe disk-shaped storage medium.
 10. The servo information writing methoddefined in claim 7 wherein the write and read heads are positionedwithin a region where an error signal obtained from the servoinformation is linear.
 11. The servo information writing method definedin claim 10 wherein the servo tracks are divided into zones, and theread write offset value is equivalent to a constant number of servotracks that exist in each zone.
 12. A servo information writing methodfor writing a burst pattern as servo information on a disk-shapedstorage medium of a data storage device that has write and read heads,comprising the steps of: calculating a read write offset value within apredetermined range on the disk-shaped storage medium, the read writeoffset value being a deviation amount between the write and read headsin a radial direction of the disk-shaped storage medium; and writing theburst pattern so that the measured read write offset value is equivalentto an integer number N of servo tracks formed by the burst pattern,wherein a pitch of the servo tracks is varied in relation to apredetermined pitch set as a standard.
 13. The servo information writingmethod defined in claim 12 wherein the integer number N increasesstepwise from an inner diameter toward an outer diameter of thedisk-shaped storage medium.
 14. The servo information writing methoddefined in claim 12 wherein the write and read heads are positionedwithin a region where an error signal obtained from the servoinformation is linear.
 15. The servo information writing method definedin claim 12 wherein the servo tracks are divided into zones, and theread write offset value is equivalent to a constant number of servotracks that exist in each zone.